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<!--ES5 变量提升和变量覆盖-->
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
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	<body>
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	<script type="text/javascript">
		var a = 123;
		function f() {
			console.log(a);
			var a = 1;
			console.log(a);
		}
		f();
	</script>
</html>
